Philadelphia chromosome-like acute lymphoblastic leukemia with concomitant rearrangements of CRLF2 and ABL1: a pediatric case report.

BACKGROUND: BCR::ABL1-like or Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) was first reported in 2009. Ph-like ALL is characterized by gene signature similar to Philadelphia chromosome ALL, but without BCR::ABL1 fusions. Molecularly, Ph-like ALL is divided into seven categories, with CRLF2 and ABL-class rearrangements being the two most common subtypes, exhibiting alterations in distinct downstream signaling cascades. CASE PRESENTATION: We report a rare case of pediatric Ph-like ALL with concomitant CRLF2 and ABL1 rearrangements. CRLF2 was fused with P2RY8, its most common fusion partner, whereas ABL1 was fused with MYO18B, a novel fusion partner that has not been previously reported. The 4-year-old female patient was treated using the national multicenter CCCG-ALL-2020 protocol with the addition of dasatinib at the end of induction when ABL1 rearrangement was confirmed by RNA-seq. Morphologically and molecularly, the patient remained in continuous remission until the last follow-up. To the best of our knowledge, this is the first case of Ph-like ALL harboring two distinct rearrangement categories. CONCLUSIONS: Our results identified that ABL1 rearrangement and CRLF2 rearrangement can coexist. The application of FISH, whole transcription sequencing, PCR can help us to have a more comprehensive understanding of ALL cytogenetics and molecular biology. Further studies are needed to explore the role of targeted therapies in such rare clinical scenarios.

Philadelphia-like acute lymphoblastic leukemia: the journey from molecular background to the role of bone marrow transplant-review article.

Philadelphia chromosome-like (Ph-like) ALL is a recent subtype of acute lymphoblastic leukemia. Although it does not express the BCR-ABL fusion gene, it has a behavior like true BCR/ABL1-positive cases. This subtype harbors different molecular alterations most commonly CRLF2 rearrangements. Most cases of Ph-like ALL are associated with high white blood cell count, high minimal residual disease level after induction therapy, and high relapse rate. Efforts should be encouraged for early recognition of Ph-like ALL to enhance therapeutic strategies. Recently, many trials are investigating the possibility of adding the tyrosine kinase inhibitor (TKI) to chemotherapy to improve clinical outcomes. The role and best timing of allogeneic bone marrow transplant in those cases are still unclear. Precision medicine should be implemented in the treatment of such cases. Here in this review, we summarize the available data on Ph-like ALL.

Clinical, biological, and outcome features of P2RY8-CRLF2 and CRLF2 over-expression in pediatric B-cell precursor acute lymphoblastic leukemia according to the CCLG-ALL 2008 and 2018 protocol.

OBJECTIVES: CRLF2 alterations are associated with B-cell precursor acute lymphoblastic leukemia (BCP-ALL). This study aimed to explore the clinical, biological, and outcome features of pediatric BCP-ALL with CRLF2 abnormalities. METHODS: This study enrolled 630 childhood BCP-ALLs treated on CCLG-ALL 2008 or 2018 protocol. P2RY8-CRLF2 was determined by Sanger sequencing and CRLF2 expression was evaluated by qRT-PCR. The correlation between clinical, biological features and outcomes with P2RY8-CRLF2 or CRLF2 over-expression were analyzed. RESULTS: P2RY8-CRLF2 and CRLF2 over-expression were found in 3.33% and 5.71% respectively. P2RY8-CRLF2 was associated with male, higher frequency of CD7 expression, high WBC and MRD before consolidation. CRLF2 over-expression showed ETV6-RUNX1- , higher frequency of CD22, CD34, CD66c, CD86 expression, hyperdiploidy and high MRD at early treatment. The lower overall survival (OS) was found in patients with P2RY8-CRLF2 and confined only in IR group. Furthermore, adverse event-free survival and OS of P2RY8-CRLF2 were discovered comparing to those without known fusions or treated on CCLG-ALL 2008 protocol. However, P2RY8-CRLF2 was not confirmed as independent prognostic factors and no prognostic impact of CRLF2 over-expression was found. CONCLUSIONS: These findings indicate P2RY8-CRLF2 identifies a subset of patients with specific features and adverse outcomes that could be improved by risk-directed treatment.

CRLF2 overexpression defines an immature-like subgroup which is rescued through restoration of the PRC2 function in T-cell precursor acute lymphoblastic leukemia.

CRLF2 overexpression has been described as a biomarker of poor prognosis in T-cell acute lymphoblastic leukemia (T-ALL). In the present study, we aimed to unravel the genomic profile underlying CRLF2 overexpression (CRLF2-high) by analyzing RNA-seq, WES, and SNP-array data from 264 T-ALL patients and five cell lines deposited on the TARGET initiative, Cancer Cell Line Encyclopedia and Gene Expression Omnibus. These data allowed us to delineate the genomic landscape of CRLF2-high in T-ALL, which was associated with PTEN, JAK3, PHF6, EZH2, and RUNX1 mutations. We also observed an enrichment of CRLF2-high in early T-precursor (ETP)-ALL (23.08% vs. 4.02%, P = 7.579e-06 ) and a very similar gene upregulation profile between these two entities. The inhibition of BET (iBET) proteins is a strategy previously demonstrated to reverse the gene upregulation pattern of ETP cells through restoration of polycomb repressive complex 2 (PRC2) activity. While CRLF2 expression was rescued by using this strategy in LOUCY (untreated vs. iBET P = 0.0095, DMSO vs. iBET P = 0.0286), a classical ETP-ALL cell line, PRC2 loss was not sufficient to promote CRLF2 upregulation in JURKAT, a more mature T-ALL cell line. Considering the role of IKZF1 in CRLF2 regulation and in recruitment of PCR2, we evaluated IKZF1 status according to CRLF2-expression subgroups. We identified that IKZF1 transcripts with intron retention were upregulated in the CRLF2-high subgroup. Here, we delineated the gene expression profile of CRLF2-high T-ALL samples and unraveled the crucial role of PRC2 in CRLF2 regulation in ETP-ALL.

High occurrence of CRLF2 abnormalities in Mexican children with B-cell acute lymphoblastic leukemia.

The P2RY8-CRLF2 and IGH-CRLF2 rearrangements induce the overexpression of cytokine receptor-like factor 2 (CRLF2) and have been associated with relapse and poor prognosis in B-cell acute lymphoblastic leukemia (B-ALL). Additionally, they are frequently documented in high-risk Hispanic populations. To better understand the potential causes of the adverse prognosis of childhood B-ALL in Mexico, we analyzed these rearrangements and the CRLF2 mRNA and protein levels in 133 Mexican children with B-ALL. We collected bone marrow samples at diagnosis and evaluated the CRLF2 gene expression by qRT-PCR and the total CRLF2 protein by flow cytometry. P2RY8-CRLF2 and IGH-CRLF2 were detected by RT-PCR and FISH, respectively. The median time of follow-up to determine the prognostic significance of the CRLF2 abnormalities was three years. In 82% of the participants, the mRNA levels correlated with the cell-surface and intracellular CRLF2 protein levels. The P2RY8-CRLF2 rearrangement was present in 31.5% (42/133) of the patients, while the IGH-CRLF2 rearrangement was detected in 13.5% (9/67) of patients with high expression of CRLF2 (6.8% of the total sample). CRLF2 copy number variations (gain) were also detected in 7.5% (5/67) of patients with high protein levels. The overall survival (OS) presented significantly lower rates in patients with high white blood cell count (≥50x109/L) regardless of CRLF2 expression, but high levels of CRLF2 gene expression appears to contribute to the reduction of OS within this group of patients. In conclusion, in our cohort, a high occurrence of CRLF2 abnormalities was documented, particularly the P2RY8-CRLF2 rearrangement, which might represent a characteristic of the Mexican population. Targeted therapy to treat this group of patients could improve OS.

Characterization of Philadelphia-like Pre-B Acute Lymphoblastic Leukemia: Experiences in Mexican Pediatric Patients.

Ph-like subtypes with CRLF2 abnormalities are frequent among Hispano-Latino children with pre-B ALL. Therefore, there is solid ground to suggest that this subtype is frequent in Mexican patients. The genomic complexity of Ph-like subtype constitutes a challenge for diagnosis, as it requires diverse genomic methodologies that are not widely available in diagnostic centers in Mexico. Here, we propose a diagnostic strategy for Ph-like ALL in accordance with our local capacity. Pre-B ALL patients without recurrent gene fusions (104) were classified using a gene-expression profile based on Ph-like signature genes analyzed by qRT-PCR. The expressions of the CRLF2 transcript and protein were determined by qRT-PCR and flow cytometry. The P2RY8::CRLF2, IGH::CRLF2, ABL1/2 rearrangements, and Ik6 isoform were screened using RT-PCR and FISH. Surrogate markers of Jak2-Stat5/Abl/Ras pathways were analyzed by phosphoflow. Mutations in relevant kinases/transcription factors genes in Ph-like were assessed by target-specific NGS. A total of 40 patients (38.5%) were classified as Ph-like; of these, 36 had abnormalities associated with Jak2-Stat5 and 4 had Abl. The rearrangements IGH::CRLF2,P2RY8::CRLF2, and iAMP21 were particularly frequent. We propose a strategy for the detection of Ph-like patients, by analyzing the overexpression/genetic lesions of CRLF2, the Abl phosphorylation of surrogate markers confirmed by gene rearrangements, and Sanger sequencing.

TSLP as a Potential Therapy in the Treatment of CRLF2 B Cell Acute Lymphoblastic Leukemia.

Cytokine receptor-like factor 2 B-cell acute lymphoblastic leukemia (CRLF2 B-ALL) is a high-risk subtype characterized by CRLF2 overexpression with poor survival rates in children and adults. CRLF2 and interleukin-7 receptor alpha (IL-7Rα) form a receptor for the cytokine thymic stromal lymphopoietin (TSLP), which induces JAK/STAT and PI3K/AKT/mTOR pathway signals. Previous studies from our group showed that low TSLP doses increased STAT5, AKT, and S6 phosphorylation and contributed to CRLF2 B-ALL cell survival. Here we investigated the role of TSLP in the survival and proliferation of CRLF2 B-ALL cells in vitro and in vivo. We hypothesized that high doses of TSLP increase CRLF2 signals and contribute to increased proliferation of CRLF2 B-ALL cells in vitro and in vivo. Interestingly, we observed the opposite effect. Specifically, high doses of TSLP induced apoptosis in human CRLF2 B-ALL cell lines in vitro, prevented engraftment of CRLF2 B-ALL cells, and prolonged the survival of +TSLP patient-derived-xenograft mice. Mechanistically, we showed that high doses of TSLP induced loss of its receptor and loss of CRLF2 signals in vitro. These results suggest that high doses of TSLP could be further investigated as a potential therapy for the treatment of CRLF2 B-ALL.

Hematological characteristics, cytogenetic features, and post-induction measurable residual disease in thymic stromal lymphopoietin receptor (TSLPR) overexpressed B-cell acute lymphoblastic leukemia in an Indian cohort.

The overexpression of cytokine receptor-like factor-2 (CRLF2) identified by anti-thymic stromal lymphopoietin receptor/TSLPR flow cytometry (FCM) has been reported as a screening tool for the identification of BCR-ABL1-like B-cell acute lymphoblastic leukemia/B-ALL with CRLF2 re-arrangement. TSLPR expression was studied prospectively in consecutive 478 B-ALLs (≤ 12 years (n = 244); 13-25 years (n = 129); > 25 years (n = 105)) and correlated with various hematological parameters and end-of-induction measurable residual disease (day 29; MRD ≥ 0.01% by 10-color FCM). TSLPR positivity in ≥ 10% leukemic cells was detected in 14.6% (n = 70) of B-ALLs. CRLF2 re-arrangement was detected in eight cases (11.4%) including P2RY8-CRLF2 (n = 6), and IgH-CRLF2 (n = 2) with a median TSLPR positivity of 48.8% and 99% leukemic cells, respectively. Recurrent gene fusions/RGF (BCR-ABL1 (17.1%); ETV6-RUNX1 (4.2%), TCF3-PBX1 (1.4%)), other BCR-ABL1-like chimeric gene fusions/CGFs (PDGFRB-rearrangement (2.9%), IgH-EPOR (1.4%)), CRLF2 extra-copies/hyperdiploidy (17.1%), and IgH translocation without a known partner (10%) were also detected in TSLPR-positive patients. CD20 positivity (52.9% vs 38.5%; p = 0.02) as well as iAMP21 (4.3% vs 0.5%; p = 0.004) was significantly more frequent in TSLPR-positive cases. TSLPR-positive patients did not show a significantly higher MRD, compared to TSLPR-negative cases (37% vs 33%). Increasing the threshold cut-off (from ≥ 10 to > 50% or > 74%) increased the specificity to 88% and 100% respectively in identifying CRLF2 translocation. TSLPR expression is not exclusive for CRLF2 translocations and can be seen with various other RGFs, necessitating their testing before its application in diagnostic algorithms. In patients with high TSLPR positivity (> 50%), the testing may be restricted to CRLF2 aberrancies, while patients with 10-50% TSLPR positivity need to be tested for both CRLF2- and non-CRLF2 BCR-ABL1-like CGFs.

From the archives of MD Anderson Cancer Center: Concurrent BCR-ABL1 and CRLF2 rearrangements in B-lymphoblast phase of chronic myeloid leukemia.

The t(9;22)(q34;q11.2), also known as the Philadelphia (Ph) chromosome, results in BCR-ABL1 fusion residing on the derivative chromosome 22. This translocation is characteristic of chronic myeloid leukemia, but also can occur in a substantial subset of B acute lymphoblastic leukemia (B-ALL) cases. Ph-like B-ALL has a gene expression profile similar to that of BCR-ABL1 positive/Ph-positive B-ALL, but by definition Ph-like B-ALL does not have the sentinel BCR-ABL1 or the Ph chromosome. About half of Ph-like B-ALL cases carry CRLF2 rearrangements. Rare cases of de novo B-ALL with co-occurrence of BCR-ABL1 and CRLF2 rearrangements have been described. To our knowledge, this is the first report of concurrent BCR-ABL1 and CRLF2 rearrangements in blast phase of chronic myeloid leukemia. In this patient, CRLF2 rearrangement was acquired at the time of disease progression to B-lymphoblast phase of chronic myeloid leukemia. We also review the literature and discuss the distinct clinicopathologic, and genomic characteristics of CRLF2 rearranged B-ALL.

[Down syndrome and acute lymphoblastic leukemia].

In an analysis of 653 cases of acute lymphoblastic leukemia associated with Down syndrome (DS-ALL) collected from clinical research groups worldwide, the 8-year disease-free survival for DS-ALL was 64%, which was worse than the 81% for non-DS-ALL during the same period. This could be because DS-ALL has less hyperdiploidy and ETV6-RUNX1 abnormalities, which have a favorable prognosis, more Ph-like ALL, which has a poor prognosis, as well as more adverse deaths due to infectious complications. It has been reported that optimizing the treatment intensity using minimal residual disease and by strengthening the measures against adverse effects improve the treatment outcome of DS-ALL. The incidence of DS-ALL is reported to be 20 times higher than that of non-DS-ALL. The mechanism is believed to be through proliferation of the lymphoid system caused by HMGN1 on chromosome 21 as well as activation of JAK-STAT and proliferation of ALL cells caused by overexpression of CRLF2, such as P2RY8-CRLF2 fusion. The CRLF2 abnormality is found in 30-60% of DS-ALL cases. In the future, treatment of CRLF2, targeting JAKs downstream of CRLF2, and administration of blinatumomab or CAR-T therapy will be incorporated into DS-ALL treatment.

[Assessment of the leukemogenic mechanism of Ph-like acute lymphocytic leukemia for the identification of a novel therapeutic target].

Ph-like acute lymphocytic leukemia (ALL) is a subtype of Ph-negative B precursor ALL, and its gene expression profile is similar to that of Ph+ALL. In recent decades, comprehensive genomic analyses have revealed that Ph-like ALL has two types. The first type is associated with the ABL-class tyrosine kinase fusion gene, and the second type with fusion genes involving cytokine receptors or molecules, including CRLF2, which are correlated with the activation of the JAK/STAT pathway. Based on these findings, tyrosine kinase or JAK inhibitors were found to be effective for Ph-like ALL. Genetic abnormalities identified in Ph-like ALL, except for CRLF2 rearrangement, are quite rare. Thus, functional studies regarding each genomic abnormality are relevant for establishing targeted therapies for Ph-like ALL. To develop a targeted molecular therapy, a functional study of NCOR1-LYN, which is a novel ABL-class fusion gene, was conducted on pediatric patients with Ph-like ALL.

Post-Essential Thrombocythemia Myelofibrosis and Multiple Isodicentric Y Chromosomes: A Unique Case among a Rare Association.

Multiple isodicentric Y chromosomes [idic(Y)] is a rare cytogenetic abnormality, most exclusively described in constitutional karyotypes. Only recently has this entity been reported in hematologic neoplasms such as myeloid disorders, albeit these cases remain very scarce. The possible involvement of increasing copies of potential proto-oncogenes located on the multiple idic(Y) led to consider one of them, CRLF2, as a target for kinase inhibitors. We report here, to our knowledge, the first case of multiple idic(Y) in a patient with myelofibrosis secondary to essential thrombocythemia. The patient received ruxolitinib therapy with initial good clinical response.

Suppressors and activators of JAK-STAT signaling at diagnosis and relapse of acute lymphoblastic leukemia in Down syndrome.

Children with Down syndrome (DS) are prone to development of high-risk B-cell precursor ALL (DS-ALL), which differs genetically from most sporadic pediatric ALLs. Increased expression of cytokine receptor-like factor 2 (CRLF2), the receptor to thymic stromal lymphopoietin (TSLP), characterizes about half of DS-ALLs and also a subgroup of sporadic "Philadelphia-like" ALLs. To understand the pathogenesis of relapsed DS-ALL, we performed integrative genomic analysis of 25 matched diagnosis-remission and -relapse DS-ALLs. We found that the CRLF2 rearrangements are early events during DS-ALL evolution and generally stable between diagnoses and relapse. Secondary activating signaling events in the JAK-STAT/RAS pathway were ubiquitous but highly redundant between diagnosis and relapse, suggesting that signaling is essential but that no specific mutations are "relapse driving." We further found that activated JAK2 may be naturally suppressed in 25% of CRLF2pos DS-ALLs by loss-of-function aberrations in USP9X, a deubiquitinase previously shown to stabilize the activated phosphorylated JAK2. Interrogation of large ALL genomic databases extended our findings up to 25% of CRLF2pos, Philadelphia-like ALLs. Pharmacological or genetic inhibition of USP9X, as well as treatment with low-dose ruxolitinib, enhanced the survival of pre-B ALL cells overexpressing mutated JAK2. Thus, somehow counterintuitive, we found that suppression of JAK-STAT "hypersignaling" may be beneficial to leukemic B-cell precursors. This finding and the reduction of JAK mutated clones at relapse suggest that the therapeutic effect of JAK specific inhibitors may be limited. Rather, combined signaling inhibitors or direct targeting of the TSLP receptor may be a useful therapeutic strategy for DS-ALL.

The Current Genomic and Molecular Landscape of Philadelphia-like Acute Lymphoblastic Leukemia.

Philadelphia (Ph)-like acute lymphoblastic leukemia (ALL) is a high-risk B-cell Acute Lymphoblastic Leukemia (B-ALL) characterized by a gene expression profile similar to Ph-positive B-ALL but lacking the BCR-ABL1 translocation. The molecular pathogenesis of Ph-like B-ALL is heterogenous and involves aberrant genomics, receptor overexpression, kinase fusions, and mutations leading to kinase signaling activation, leukemogenic cellular proliferation, and differentiation blockade. Testing for the Ph-like signature, once only a research technique, is now available to the clinical oncologist. The plethora of data pointing to poor outcomes for this ALL subset has triggered investigations into the role of targeted therapies, predominantly involving tyrosine kinase inhibitors that are showing promising results.

CRLF2 expression associates with ICN1 stabilization in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematopoietic malignancy with few molecular alterations showing a consensual prognostic value. CRLF2 overexpression was recently identified in high-risk T-ALL patients. For these cases, no genomic abnormality was found to be associated with CRLF2 overexpression. IKZF1 has been recently shown to be a direct transcriptional regulator of CRLF2 expression. Moreover, it is known that NOTCH1 antagonizes IKZF1 in T-ALL. In light of these pieces of evidence, we reasoned that IKZF1 binding perturbation and CRLF2 upregulation could be associated in T-ALL. We evaluated two independent series of pediatric T-ALL cases (PHOP, n = 57 and TARGET, n = 264) for the presence of common T-ALL molecular abnormalities, such as NOTCH1/FBXW7 mutations. We also assessed CRLF2 and IKZF1 gene expression. CRLF2 overexpression was observed in 14% (PHOP) and 16% (TARGET) of T-ALL patients. No correlation was found between mRNA expression of CRLF2 and IKZF1 in both cohorts. Interestingly, we show that patients with mutations affecting NOTCH1-PEST domain and/or FBXW7 had higher CRLF2 expression (P = .04). In summary, we demonstrate for the first time that only mutations resulting in ICN1 (intracellular domain of NOTCH1) stabilization are associated with CRLF2 overexpression.

GATA3 germline variant is associated with CRLF2 expression and predicts outcome in pediatric B-cell precursor acute lymphoblastic leukemia.

The germline variant at rs3824662 in GATA3 is a risk locus for Philadelphia-like acute lymphoblastic leukemia (Ph-like ALL), the biological subtype of B-cell precursor (BCP)-ALL defined by a distinct gene expression profile and the presence of specific somatic aberrations including rearrangements of CRLF2. In this study, we investigated whether rs3824662 in GATA3 associates with CRLF2 expression in leukemic cells and predicts prognosis in pediatric BCP-ALL patients treated according to the ALL Intercontinental Berlin-Frankfurt-Münster (IC BFM) 2009 (n = 645) and the ALL IC BFM 2002 (n = 216) protocols. High expression of CRLF2 was observed at both protein and mRNA levels (fourfold higher in AA than in CA + CC) among GATA3 AA variant carriers, independent of the presence of P2RY8-CRLF2 fusion. Additionally, the AA variant at rs3824662 was a significant factor affecting minimal residual disease level at the end of induction phase and overall survival regardless of the risk group and the protocol. The germline variant at rs3824662 in GATA3 is a prognostic factor which associates with CRLF2 expression in leukemic cells supporting the hypothesis that GATA3 may have a regulatory effect on the CRLF2 pathway in pediatric BCP-ALL.

[Detection of activating mutations in RAS/RAF/MEK/ERK and JAK/STAT signaling pathways].

ISSUE: The study of activating mutations (NRAS,KRAS,FLT3,JAK2,CRLF2genes) of RAS/RAF/MEK/ERK and JAK/STAT signaling pathways in B-cell acute lymphoblastic leukemia (B-ALL) in adult patients which are included in Russian multicenter clinical trials. MATERIALS AND METHODS: Within the multicenter study there were 119 adult patients included withde novoB-ALL. The study was considered as prospective and retrospective. The group withBCR-ABL1-negative B-ALL consisted of up to 93 patients (45 male and 48 female, at the age of 17 to 59, the median age 31), they were treated according to the protocols ALL-2009, ALL-2016. The median follow-up lasted for 19 months (1119). The group withBCR-ABL1-positive B-ALL with up to 26 patients (10 male and 16 female, at the age of 23 to 78, the median age 34 years) was included in the study as well. The treatment was carried out according to the protocols ALL-2009 and ALL-2012 in combination with tyrosine kinase inhibitors. The median follow-up lasted for 23 months (4120). The molecular analysis of activating mutations inNRAS,KRASgenes (RAS/RAF/MEK/ERK signaling pathway) andJAK2,CRLF2genes (JAK/STAT signaling cascade) was performed via Sanger sequencing. The internal tandem duplications (ITDs) inFLT3gene were studied by fragment analysis. The evaluation of CRLF2 expression was fulfilled via flow cytometry. RESULTS: Activating mutations inNRAS,KRAS,FLT3genes were found in 22 (23.6%) patients withBCR-ABL1-negative B-ALL. In total, 23 mutations were revealed in theNRAS(n=9),KRAS(n=12), andFLT3(n=2) genes, according to statistics that was significantly more frequent than withBCR-ABL1-positive B-ALL, these genes mutations were not identified in patients (p=0.007). The frequency of mutations detection inKRASandNRASgenes in patients withBCR-ABL1-negative B-ALL was comparable as 12.9% (12 of 93) to 9.7% (9 of 93), respectively (p=0.488). One patient was simultaneously revealed 2 mutations in theKRASgene (in codons 13 and 61).FLT3-ITD mutations were detected in 3.5% (2 of 57) cases ofBCR-ABL1-negative B-ALL. In patients withBCR-ABL1-positive B-ALLFLT3-ITD mutations were not assessed. Violations in the JAK/STAT signaling cascade were detected in 4 (4.3%) patients withBCR-ABL1-negative B-ALL. They were represented by the missense mutations ofJAK2gene (n=3) and the overexpression of CRLF2 (n=2); in one patient were detected the overexpression of CRLF2 and a mutation inJAK2gene simultaneously. No mutations were found inCRLF2gene. In patients withBCR-ABL1-positive B-ALL noJAK2mutations were detected. As long as analyzing demographic and clinical laboratory parameters between groups of patients with and without mutations, there were no statistically significant differences obtained. In the analyzed groups of patients, long-term therapy results did not differentiate according to the mutations presence inNRAS,KRAS,FLT3,JAK2genes. Also, substantive differences were not shown in the rate of the negative status achievement of the minimum residual disease between patients with and without activating mutations in the control points of the protocol (on the 70th, 133rd and 190th days). CONCLUSION: NRAS,KRAS,FLT3,JAK2activating mutations do not affect the long-term results of the therapy and the rate of the negative status achievement of the minimum residual disease in patients withBCR-ABL1-negative B-ALL treated by the Russian multicenter clinical trials.

A risk score including microdeletions improves relapse prediction for standard and medium risk precursor B-cell acute lymphoblastic leukaemia in children.

To prevent relapse, high risk paediatric acute lymphoblastic leukaemia (ALL) is treated very intensively. However, most patients who eventually relapse have standard or medium risk ALL with low minimal residual disease (MRD) levels. We analysed recurrent microdeletions and other clinical prognostic factors in a cohort of 475 uniformly treated non-high risk precursor B-cell ALL patients with the aim of better predicting relapse and refining risk stratification. Lower relapse-free survival at 7 years (RFS) was associated with IKZF1 intragenic deletions (P < 0·0001); P2RY8-CRLF2 gene fusion (P < 0·0004); Day 33 MRD>5 × 10-5 (P < 0·0001) and High National Cancer Institute (NCI) risk (P < 0·0001). We created a predictive model based on a risk score (RS) for deletions, MRD and NCI risk, extending from an RS of 0 (RS0) for patients with no unfavourable factors to RS2 +  for patients with 2 or 3 high risk factors. RS0, RS1, and RS2 +  groups had RFS of 93%, 78% and 49%, respectively, and overall survival (OS) of 99%, 91% and 71%. The RS provided greater discrimination than MRD-based risk stratification into standard (89% RFS, 96% OS) and medium risk groups (79% RFS, 91% OS). We conclude that this RS may enable better early therapeutic stratification and thus improve cure rates for childhood ALL.

Molecular characterization of acute lymphoblastic leukemia with high CRLF2 gene expression in childhood.

BACKGROUND: A high-level expression of the CRLF2 gene is frequent in precursor B-cell acute lymphoblastic leukemia (pB-ALL) and can be caused by different genetic aberrations. The presence of the most frequent alteration, the P2RY8/CRLF2 fusion, was shown to be associated with a high relapse incidence in children treated according to ALL-Berlin-Frankfurt-Münster (BFM) protocols, which is poorly understood. Moreover, the frequency of other alterations has not been systematically analyzed yet. PROCEDURE: CRLF2 mRNA expression and potential genetic aberrations causing a CRLF2 high expression were prospectively assessed in 1,105 patients treated according to the Associazione Italiana Ematologia Oncologia Pediatrica (AIEOP)-BFM ALL 2009 protocol. Additionally, we determined copy number alterations in selected B-cell differentiation genes for all CRLF2 high-expressing pB-ALL cases, as well as JAK2 and CRLF2 mutations. RESULTS: A CRLF2 high expression was detected in 26/178 (15%) T-cell acute lymphoblastic leukemia (T-ALL) cases, 21 of them (81%) had been stratified as high-risk patients by treatment response. In pB-ALL, a CRLF2 high expression was determined in 91/927 (10%) cases; the P2RY8/CRLF2 rearrangement in 44/91 (48%) of them, supernumerary copies of CRLF2 in 18/91 (20%), and, notably, the IGH/CRLF2 translocation was detected in 16/91 (18%). Remarkably, 7 of 16 (44%) patients with IGH/CRLF2 translocation had already relapsed. P2RY8/CRLF2- and IGH/CRLF2-positive samples (70 and 94%, respectively) were characterized by a high frequency of additional deletions in B-cell differentiation genes such as IKZF1 or PAX5. CONCLUSION: Our data suggest that this high frequency of genetic aberrations in the context of a high CRLF2 expression could contribute to the high risk of relapse in P2RY8/CRLF2- and IGH/CRLF2-positive ALL.